The invention relates to a layer system for the formation of a surface on a substrate, to a vaporization source for the manufacture of a layer system and also to a substrate, in particular to a tool having a layer system in accordance with the invention, all in accordance with the preambles of the independent claims of the respective categories.
The manufacture of performance tools and components is mainly realized by the coating of their surfaces. An important class of such coated substrates are tools, among other things in particular chip-forming tools and also components and machine parts for machines which are subject to wear in all possible embodiments. Typical substrate materials which are coated are among other things tool steels and hard metals but also all other possible substrate materials.
A known problem in the coating of these materials is that they have a relatively high oxidation rate in air at around 500° C. and soften at relatively low temperatures (ca. 500° C. for HSS and 650° C. for a hard metal).
Accordingly, ceramic cutting bodies are also preferably used, for example on the basis of cubic boron nitride for the hard machining of steels. Thus, the most diverse SiN ceramics are, for example, used for the high speed machining of aluminum alloys and grey cast ion. The ceramics prove to be substantially more durable in comparison to metallic tool materials. A further increase in performance can be achieved by suitable coating of the tools.
The hard material layers known from the prior art are in this respect frequently based on the classic compounds such as TiN, TiNC, CrN. These known hard layers do however have their limits with respect to their field of use above all with respect to their ability to work at high temperatures. On the one hand, the hardness drops off notably at elevated temperatures and, on the other hand, oxidation already sets in at relatively low temperatures and can lead to an increased layer wear at the temperature of use.
In order to avoid these problems essentially two layer classes have been developed which have oxidation resistance in the range up to 1000° C. and also have improved characteristics with respect to the hardness.
The one layer class relates to Al containing base layers such as AlTiN and AlCrN to which additional elements can be alloyed depending on the requirement. Typical compounds from this area are compounds of the form AlTiX-NCO, wherein X is, for example, Cr or another metal.
Another route followed in the prior art for the performance increase of coated tools consists in the combination of classic hard material layers as a carrier layer combined with finish layers as a functional layer. The high silicon containing layers (10 at-% or more); at-% signifies in the context of this application “atomic percent” of the type MeSiXNCO layer (X is further metals or B) are to be named, such as TiSN which have a significantly improved ability to withstand the temperature loading.
In addition it is furthermore known for example to deposit oxidic ceramic layers such as Al2O3 by means of CVD processes on indexable or reversible cutting inserts in order to be able to counteract wear processes at elevated contact temperatures in particular during turning.
In addition boron based layers such for example B4C and also cubic BN layers are at the stage of research. However, cubic BN has the decisive disadvantage that is extremely complicated to present. This is above all due to difficulties of the layer growth itself but also brought about by too high inherent stresses in the layers.
In the field of high temperature materials bulk ceramics on the basis of SiCN have been produced in recent years which are characterized by high hardness and an improvement of the resistance to oxidation in relation to SiC and Si3N4. Their special characteristics are based on the complex covalent chemical bonds and the low diffusion rate of oxygen in the amorphous structure of SiCN.
However, despite all previous efforts, the provision of coatings has only partly succeeded which are able to meet increasingly higher demands on the mechanical characteristics such as for example the hardness, residual compressive stress and toughness, tribological characteristics such as tendency to adhesion at higher temperatures and also friction, the oxidation resistance, phase stability and other characteristic properties, above all also at extreme temperatures.
Moreover, the above-described higher performance layers can also only be manufactured with great difficulties from the technical method view point and the tools coated therewith are very expensive, so that, however, when considered from the point of view economy, coating is in many cases not worth while or such coated tools only have a restricted market.